The present invention relates to a method of pseudo-randomly shuffling a Hadamard function in a wireless CDMA system to dramatically improve performance.
Wireless communications has emerged to become a huge market as millions of people world-wide buy cellular handsets, subscribe to Personal Communications Services (PCS), and make calls on a daily basis. There are many competing technologies in the wireless communications field. Initially, cellular transmissions were made according to traditional analog radio frequency (RF) technology. But as wireless digital technology improved, it became clear that digital applications were far superior to that of analog. The three dominant wireless digital technologies existing today include Global System of Mobile communications (GSM), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). Of these three digital wireless technologies, CDMA is gaining widespread popularity because of its many advantages.
Generally, CDMA offers greater signal quality, resulting in clearer calls. In addition, CDMA utilizes a spread-spectrum approach, which makes it ideal for deployment in dense urban areas where multi-pathing is an issue. This results in fewer dropped calls. Furthermore, CDMA technology is more power efficient, thereby prolonging the standby and active battery life. But one of the most attractive features of CDMA is that it offers a greater capacity for carrying signals. Basically, the airwaves are divided into a number of different frequency bands per Federal Communications Commission (FCC) regulations. A limited segment of the airwaves has been allocated by the FCC for cellular usage. Due to the huge demand for cellular usage and the limited bandwidth that is available, getting a license from the FCC to transmit on a particular frequency band is extremely expensive. By increasing capacity, CDMA enables PCS providers to carry more users per channel. This increased capacity directly translates into greater revenue for cellular companies.
The advantages of CDMA carry over into high-speed wireless digital access. Increasingly, wireless digital applications are being used to access digital data (e.g., the Internet, intranet, multimedia, business data, etc.) at high speeds. With high speed wireless access, mobile users can obtain instant access to the Internet, business data (e.g., stock market quotes, sales reports, inventory information, price checks, customer data, emails, pages, etc.), and other real time data (e.g., traffic updates, weather information, sports news, etc.). The goal is to provide cellular handsets, personal digital assistants, portable communications devices, etc. the ability to transmit and receive digital data as well as make conventional telephone calls. The trend is towards ever faster mobile data speeds to meet customer demands. With greater data speeds, it is possible to provide even more data to more users. Recent CDMA based standards such as IS-95 and 3G are proposing increased data rates and capabilities. Although CDMA offers superior capacity over that of competing wireless analog and digital technologies, the capacity at which data can be conveyed is approaching the maximum bounds that can be delivered by conventional CDMA technology.
Therefore, there is a need to somehow increase the capacity at which data can be delivered through wireless digital technology. The present invention provides a unique, novel solution which improves the capacity of CDMA by a factor of four.
The present invention pertains to a method of pseudo-randomly shuffling the rows of a Hadamard function in a wireless CDMA system to dramatically improve performance. A Hadamard function is used to provide orthogonality between users. The orthogonal waveforms are used to prevent interference from different users sharing the same cell and to allow the bandwidth from multiple channels to be aggregated. The rows of the Hadamard function are shuffled in a pseudo-random manner. This effectively maximally spreads the spectral density of the transmitted signal out across the available spectrum. Sets of these pre-computed pseudo-randomly shuffled Hadamard codes are stored in lookup tables of mobile wireless devices. During transmission, a code is supplied by the lookup table, and the data signal is then modulated by that particular code. Consequently, by aggregating multiple orthogonal channels, one data bit can be transmitted per chip, which substantially improves the rate by which data can be transmitted. The receiver then demodulates the received signal by a corresponding code stored in its lookup table.